1. Field of the Invention
The present invention relates to a magnetic disk driving apparatus for magnetically writing and reading digital information, and more particularly, to a velocity and position estimator of a magnetic head (or a data transducer) upon a track seek.
2. Description of the Related Art
A magnetic disk driving apparatus for magnetically writing and reading data on a rotary magnetic disk can access a large amount of data at a high speed, and thus, it is widely used as an auxiliary memory of a computer system. In the magnetic disk driving apparatus, data is stored in tracks which extend radially along the magnetic disk surface. These tracks are accessed by a magnetic head for reading, writing and erasing data on the magnetic disk.
The magnetic head is moved in a radical direction along the magnetic disk surface under the control of a head position servo mechanism capable of positioning the magnetic head on any one selected track. In order to selectively position the magnetic head on a specific track, a current track position of the magnetic head must be monitored. As stated above, servo information indicative of the track position of the magnetic head is provided by using a specific servo pattern which is read from the magnetic disk surface by means of the magnetic head. The servo pattern is permanently written on the magnetic disk surface after assembly of the magnetic disk driving apparatus. Upon accessing the data on the magnetic disk surface, the servo pattern is detected by the magnetic head and used as track position information. An embedded servo method is an example of a method that provides the servo position information. In the embedded servo system, the servo information is arranged reciprocally between data intervals on the magnetic disk surface. Each portion of servo information includes track position information, a track address, and index information, as well as other information stored on the disk.
The magnetic head is positioned on a specific track by using the servo information through two steps known as track seek and track follow. The track seek step is performed by moving the magnetic head from the current track to the desired track, that is, by finding the track address of the desired track and moving the magnetic head. Also, the track follow step is performed by precisely following the specific track. Thus, when the magnetic head is positioned on a given tracks, the track follow step enables the magnetic head to follow a central line of the specific track, and thereby accurately perform a read and write operation. For example, for track following in the conventional magnetic disk driving apparatus utilizing the embedded servo method, two bursts per track are effected by providing ones written beforehand as the track position information of the servo information on each side of a central line of one track on the magnetic disk surface. As a result, an amount of deviation and a deviation status representative of the magnetic head's position relative to the center of the track can be determined from the difference value. A signal indicative of the amount of deviation and deviation status of the magnetic head is typically referred to as "a position error signal" (hereinafter, referred to as a PES). The magnetic disk driving apparatus controls the magnetic head so that it is capable of following the center of the track by utilizing the PES which has values corresponding to deviations in the position of the magnetic head with respect to the center of the track.
Sakamoto, et al., Servo Motor Controlling Method, U.S. Pat. No. 4,956,593, discloses a servo motor controlling method in which the gain is varied in accordance with the rotational speed of the servo motor. I have discovered however, that the gain is not correctly varied in accordance with the specific performance of either the head or its actuator.
Sidman, Dynamic Filter For A Moving Head Disk Storage System, U.S. Pat. No. 4,172,267, discloses a dynamic filter for a moving head disk storage system which varies the gain in response to the carriage velocity. I have found however, that Sidman teaches that the gain is reduced at a low velocity and increased at a high velocity.
Three references to Hashimoto and the Asai reference, U.S. Pat. Nos. 4,965,501 entitled Servo Circuit, 5,173,647 entitled Servo Positioning Circuit, 5,194,788 entitled Servo Circuit, and 5,010,425 entitled Access Controller For Controlling The Seek Operation Of A Head Relative To A Recording Medium, each disclose servo control systems in which the gain is varied in dependence upon various detected values which bear a relationship to the velocity. I have found however, that as with Sakamoto, et al., the gain is not accurately varied in accordance with specific relationships characterizing the position and movement of the head.